Within this application several publications are referenced by Arabic numerals within parentheses. Full citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications in their entirety are hereby incorporated by reference into this application in order to more fully describe the state of the art to which this invention pertains.
Iron deficiency anemia (IDA) and Thalassemia Trait (TT) are the common causes of hypochromic microcytosis. Differentiation between these diseases is based on the measurement of serum iron, total iron binding capacity and/or the serum ferritin for IDA; and when the iron status is normal, estimation of Hb fractions, by electrophoresis for example, is required for TT. However, these procedures are complicated and expensive, especially when, in addition, alpha (.alpha.) Thalassemia Trait (.alpha.-thal) is considered. In some cases, it may require globin chain synthesis rate determination or even .alpha. globin gene analysis.
Hematological analysis has been relying on the red blood cell (RBC) indices which were first introduced by Wintrobe.sup.(1) in 1929. These include the mean corpuscular or cell volume (MCV), mean corpuscular or cell hemoglobin (MCH) and mean corpuscular or cell hemoglobin concentration (MCHC). MCV is an estimate of the average RBC volume expressed in femtoliter (fl) or 10.sup.-15 L, whereas MCH is a real quantity, where the hemoglobin (Hb) content of the average red blood cell.sup.(2) is expressed in picograms (pg) or 10.sup.-12 g. MCHC is defined as the hemoglobin concentration in the average RBC, that is understood to be the amount of Hb within the average RBC volume in which it is contained..sup.(2) The MCHC value is calculated by dividing Hb concentration of blood (grams/liter) by the hematocrit value (liter/liter). MCHC is usually reported in grams/liter (g/L) or grams/deciliter (g/dl).sup.(3).
The MCHC index has been widely accepted as a "natural" constant, not only in man but also elsewhere in the animal kingdom. Furthermore, this value varies very little even under pathological conditions. Therefore, a drastic diminution of concentration by say 30%, such as would be caused by severe iron deficiency is regarded as highly significant. Since Wintrobe, several different formulae have been introduced to discriminate between blood iron deficiency and Thalassemia Minor.
England and Fraser.sup.(4,5) proposed a linear Discriminant Function (DF) derived from the Mean Corpuscular Volume (MCV), Red Blood Corpuscle (RBC), and hemoglobin (Hb) concentration. Accordingly, the equation for DF is MCV-RBC-(5.times.Hb)-k, where k is a constant determined by the method used to calibrate the cell counter: Positive DF values are alleged to indicate IDA and negative values, TT. Mentzer.sup.(6) proposed that simple index derived from the ratio, MCV/RBC, was also capable of distinguishing the two conditions, with values below 13 indicating TT. Shine and Lal.sup.(7) introduced the expression (MCV).sup.2 .times.MCH (Mean Cell Hemoglobin) to screen for TT, where values of less than 1530 were regarded as diagnostic of this condition. Another formula is the Discrimination Score (DS),.sup.(8) based on the expression (0.096.times.MCV)+(0.415.times.RDW)-(0.139.times.RBC)-12.722 for the male, and the expression (0.096.times.MCV)+(0.415.times.RDW)-12.722 for the female, with 0.3095 as cutoff point, below which TT is probable and above which IDA is considered likely.
However, all of the above approaches have significant limitations. Firstly, their incorporation in CBC hemogram is impractical because the mathematical procedures are elaborate and apply only to one category of RBC changes. Secondly, the sensitivity and specificity of the calculations are not high, resulting in significant imprecision in discriminating between IDA and TT. Accordingly, there is still a need for a simple and effective way to discriminate between these conditions.
Therefore it is an object of this invention to provide new parameters for the determination of the average amount of hemoglobin per red corpuscle. It is another object of this invention to use the new parameters for screening RBC, which would provide useful information more directly and simply from the hematology data picture of a patient for the differentiation between IDA and TT.